1. Field of the Invention
The present invention relates to a color image forming apparatus such as color electrophotographic copying apparatus, color printer or the like. More particularly, it is concerned with a color image forming apparatus including a developing device comprising a plurality of developing units, the developing units developing an electrostatic latent image formed on a latent image bearing member. In the invention, developing means of the color image forming apparatus is applicable not only to a full-color development but also to a two-color or multicolor development. However, a full-color copying apparatus will be exemplified in the following description.
2. Description of the Prior Art
The full-color copying apparatus normally has a developing device provided with developing units containing four kinds of developers, black, magenta, yellow and cyan each. However, documents are mostly printed in black, and hence the black developer is consumed considerably much as compared with those of other colors.
Meanwhile, each developing unit of the developing device is constructed to contain the developer equally in quantity, therefore the black developer must particularly be supplemented more frequently than those of the other colors, which is something that takes a great deal of time for operators to accomplish.
A prior art attempt to solve such disadvantages, features a color image forming apparatus having a developing device wherein a developing unit for containing a black developer is larger than those for containing other color developers. An arrangement of this sort is disclosed in Japanese Patent Laid-Open Publication No. 143070/87.
However, according to the prior art color image forming apparatus, users who use a developer of color other than black (e.g., magenta or yellow developer) more than the black developer will never be satisfied thereby.
On the other hand, if all the developing units are enlarged so as to each contain a large volume of developer, then the developing device gets large in size as a whole, and thus the color image forming apparatus becomes inevitably large.